White balance adjustment method, image sensing apparatus, program, and storage medium

ABSTRACT

An object of this invention is to always obtain accurate white balance regardless of photographing conditions. To achieve this object, a white balance adjustment method includes a first color temperature calculation step of calculating a first color temperature from an image signal within a white detection range out of image signals from an image sensing element, a second color temperature calculation step of calculating a second color temperature from an image signal within a chromatic color detection range out of image signals from the image sensing element, and a white balance adjustment step of adjusting white balance on the basis of the first and second color temperatures.

FIELD OF THE INVENTION

The present invention relates to a technique of adjusting the whitebalance of an image pickup apparatus such as a digital camera or digitalvideo camera.

BACKGROUND OF THE INVENTION

The white balance device of a conventional image sensing apparatus willbe explained.

An image signal output from an image sensing element is converted into adigital signal via an A/D converter. The digital signal output from theimage sensing element is divided into an arbitrary number of blocks. Foreach block, color evaluation valuesCx=(R−B)/YCy=(R+B−2G)/YY=(R+G+B)/2are calculated (example of transformations for primary color signals).

A block where a preset white detection range to be described latercontains color evaluation values (Cx and Cy) is assumed to be white. Theintegral values (SumR, SumG, and SumB) of color pixels of the blockassumed to be white are calculated. White balance gains are calculatedfrom these integral values:kWB _(—) R=1.0/SumRkWB _(—) G=1.0/SumGkWB _(—) B=1.0/SumB

FIG. 2 is a graph showing an example of the white detection range. Whiteis sensed every arbitrary color temperature step under a light sourceranging from a high color temperature to a low color temperature. Acolor evaluation value is calculated from a signal value obtained by animage sensing element, and plotted. As is represented by (a) in FIG. 2,a white determination line from a high color temperature to a low colortemperature is obtained. In practice, even white slightly varies inspectral characteristics, and the line is given a small margin.

The conventional white balance detection device suffers the followingproblem.

For example, when a human skin is sensed by close-up under ahigh-color-temperature light source such as sunbeams, the colorevaluation value of a white object under the sun distributes like (Whitein FIG. 2). The color evaluation value of the human skin distributes atalmost the same position as that of the white color under alow-color-temperature light source, like (Skin in FIG. 2). For a largearea of the skin color, the light source is misjudged as alower-color-temperature light source than an actual one.

To avoid such misjudgment, the conventional white balance device isdesigned not to detect a low-color-temperature light source by narrowingthe white detection range to a range “White” on the assumption thatlight is external light for a high object illuminance at highpossibility.

However, the conventional white balance device cannot cope with a veryhigh illuminance of tungsten light in a studio or the like, whose colortemperature is low. For a dark object in the shade or evening, the whitebalance device must detect light sources from a high-color-temperatureone to a low-color-temperature one. The white detection range must bewidened, and misjudgment caused by a deviation to the skin color cannotbe prevented.

SUMMARY OF THE INVENTION

The present invention has been made to overcome the conventionaldrawbacks, and has as its object to always obtain accurate white balanceregardless of photographing conditions.

To solve the above problems and achieve the above object, according tothe first aspect of the present invention, a white balance adjustmentmethod is characterized by comprising a first color temperaturecalculation step of calculating a first color temperature from an imagesignal within a white detection range out of image signals from an imagesensing element, a second color temperature calculation step ofcalculating a second color temperature from an image signal within achromatic color detection range out of image signals from the imagesensing element, and a white balance adjustment step of adjusting whitebalance on the basis of the first and second color temperatures.

According to the second aspect of the present invention, a program ischaracterized by causing a computer to execute the white balanceadjustment method.

According to the third aspect of the present invention, a storage mediumis characterized by computer-readably storing the program.

According to the fourth aspect of the present invention, an imagesensing apparatus is characterized by executing the white balanceadjustment method.

Other objects and advantages besides those discussed above shall beapparent to those skilled in the art from the description of a preferredembodiment of the invention which follows. In the description, referenceis made to accompanying drawings, which form a part hereof, and whichillustrate an example of the invention. Such example, however, is notexhaustive of the various embodiments of the invention, and thereforereference is made to the claims which follow the description fordetermining the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the schematic arrangement of an imagesensing apparatus having a white balance device according to anembodiment of the present invention;

FIG. 2 is a graph showing white and skin detection axes (areas);

FIG. 3 is a view showing a color detection block;

FIG. 4 is a view showing a skin determination block; and

FIG. 5 is a flow chart showing the operation of the white balance devicein the first embodiment.

FIG. 6 is a graph showing a relation between SumCx and colortemperature.

FIG. 7 is a flow chart showing the operation of the white balance devicein the second embodiment.

FIG. 8 is a graph showing white and skin detection axis (areas).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described belowwith reference to the accompanying drawings.

(First Embodiment)

FIG. 1 is a block diagram showing the schematic arrangement of an imagesensing apparatus having a white balance device according to the firstembodiment of the present invention.

In FIG. 1, light having passed through a lens 18 is received by a CCD19, and an output signal from the CCD is converted into a digital signalvia an A/D converter 20. The white balance is adjusted by a WB circuit 6according to the first embodiment of the present invention. A colorsignal generation circuit 21 generates color difference signals U and V,and a luminance signal generation circuit generates a luminance signalY, obtaining a color image.

FIG. 2 and FIG. 8 are graphs showing a white detection range and skincolor detection range. This embodiment will exemplify an image sensingelement using a primary color filter.

In FIG. 2, an area shown as “White” is indicative of an area in whichwhite signal is detected from a picked up image in a light source whosetemperature is high. And an area shown as “Skin” is indicative of anarea in which skin color signal is detected from a picked up image in alight source whose temperature is high.

In FIG. 8, an area shown as “White” is indicative of an area in whichwhite signal is detected from a picked up image in a light source whosetemperature is low. And an area shown as “Skin” is indicative of an areain which skin color signal is detected from a picked up image in a lightsource whose temperature is low.

The white detection range is obtained by calculatingCx=(R−B)/YCy=(R+B−2G)/YY=(R+G+B)/2  (1)from output values from an image sensing element which has photographedthe white color at arbitrary steps from a high color temperature to alow color temperature, and plotting the calculated values alongtwo-dimensional axes ((a) in FIG. 2). In FIG. 2, the X-axis correspondsto the color temperature of the light source, and the Y-axis correspondsto a correction amount in the green direction. After this method, thewhite detecting area is set previously.

The skin color detection range is also obtained by photographing a humanskin at each color temperature and plotting the resultant values alongthe axes ((b) in FIG. 2). The skin color includes various colors such aswhite, black, and yellow. However, the value of hue is almost the samefor each human skin, and the skin detection axis is created using analmost intermediate skin color. The skin detecting area is made byexpanding the axes (b) in Y-axis.

An operation of detecting the white balance by using these detectionaxes according to the first embodiment will be explained with referenceto the flow chart shown in FIG. 5.

One frame shown in FIG. 3 is divided into blocks of an arbitrary size.For each block, white evaluation values (Cx and Cy) are calculated basedon color signals from an image sensing element. Whether the whiteevaluation values fall within the white detection range or skindetection range in FIG. 2 is checked.

Integral values SumRw, SumGw, and SumBw of output values from respectivecolor filters of a block falling within the white detection range, and atotal number SampleWNum of samples are calculated:SumRw=ΣR(i)SumGw=ΣG(i)SumBw=ΣB(i)SampleWNum=ΣSample(i)  (2)

White evaluation values SumCxW and SumCyW are calculated from theintegral values:SumCxW=(SumRw−SumBw)/YwSumCyW=(SumRw+SumBw−2SumGw)/YwYw=(SumRw+SumGr+SumBg)/2  (3)

The color temperature (CTempFromWhite) of the object (field of view) ispredected from these white evaluation values (step S1). Since the X-axisfor the white detection axis corresponds to the color temperature, thecolor temperature of the light source can be calculated as far as Cx isknown.

Similarly, the integral values of output values from respective colorfilters of a block falling within the skin detection range, and thetotal number of samples are calculated:SumRskin, SumGskin, SumBskin, SampleSkinNum  (4)

Skin evaluation values SumCxSkin and SumCySkin are calculated from theseintegral values:SumCxSkin=(SumRskin−SumBskin)/YskinSumCySkin=(SumRskin+SumBw−2SumGskin)/YskinYskin=(SumRskin+SumGw+SumBskin)/2  (5)

The color temperature (CTempFromSkin) of the object (field of view) ispredected from these skin evaluation values (step S2).

FIG. 6 shows the relation between SumCx and color temperature forexplaining the method to predict each color temperature from SumCxW orSumCxSkin obtained in Step S2.

L1 in FIG. 6 is used in case of obtaining color temprature“CtempFromWhite”from SumCxW.L1: Ctemp=α×SumCx+m  (6)(α: negative coefficient, m: approximately 4000K)

L2 in FIG. 6 is used in case of obtaining color temperature“CtempFromSkin” from SumCx Skin.L2: Ctemp=α×SumCx+n(n>m)  (7)

In addition, L1 in FIG. 6 is obtained previously by plotting values ofSumCx corresponding that a white object such a white paper is picked upin each different color temperature. And L2 in FIG. 6 is obtainedpreviously by plotting values of SumCx corresponding that a skin objectis picked up in different color.

The color temperature calculated from the white evaluation values andthe color temperature calculated from the skin evaluation values arecompared (step S3).

If an accurate color temperature is detected by white detection,CTempFromWhite≧CTempFromSkin  (8)(YES in step S3). The color temperature of the white detection resultcan be determined as a final color temperature of the light source (stepS4). Also when the color temperature of the white detection result ishigher than that of the skin detection result, the color temperature ofthe white detection result can be determined as a final colortemperature of the light source.

If the skin color occupies a large area regardless of the value of colortemperature, the skin color signal distributes much on the low colortemperature side along the white detection axis, thereforeCTempFromWhite as the value predicted from the white detecting area issmaller than CTempFromSkin predicted from the skin detecting area.CTempFromWhite<CTempFromSkin  (9)(NO in step S3). This represents a deviation to the skin color. In thiscase, the skin detection result is output (step S5).

In case of picking up an image in low color temperature, a white imagesignal will be detected in the skin detecting area even if a skin objectisn't in an image. Therefore that case will result in (9). However, theobtained color temperature “CtempFromSkin” from skin detecting area hasno effect on a conclusive result of an obtained color temperature“CtempResult”by getting weighted average between CtempFromWhite andCtempFromSkin, as described below.

However, digital switching between the white detection result and theskin detection result may cause white balance switching owing to a smallscene shift. To prevent this, processing of calculating the weightedaverage of two coefficients at the ratio of the number of skin-detectedsamples (this processing will be referred to as sample count coefficientmixing hereinafter) is preferably executed. Sample count coefficientmixing processing will be exemplified.

AllSampleNumber represents the total number of blocks. The occupationpercentage of the skin to the frame is determined from the sum ofskin-detected sample points:SkinSamplePercent=SampleSkinNum×100/AllSampleNumber  (10)

The final object color temperature is calculated usingSkinSamplePercent:CTempResult=k×CTempFromSkin+(1−k)×CTempFromWhite  (11)

For example, for SkinSamplePercent≧10%, the skin detection result isused by 100% (k=1). For SkinSamplePercent<10%, the white detectionresult is gradually mixed. For SkinSamplePercent=5%, 50% (k=0.5) of theskin detection result and 50% of the white detection result are mixed.For SkinSamplePercent=0%, 0% (k=0) of the skin detection result and 100%of the white detection result are mixed.

White balance process is performed based on the coefficients obtainedlike that (Step S6).

In addition, weighted average between CtempFromWhite and CtempFromSkinmay be obtained not only in case of CtempFromWhite<CtemFromSkin, butalso in case of CtempFromWhite≧CtempFromSkin. This process is simplerthan the process as described above.

As described above, the present embodiment can properly perform toadjust white balance of a picked up image regardless of colortemperature of light source and detection of skin signals in the pickedup image.

(Second Embodiment)

The second embodiment is different from the first embodiment in themethod of mixing an object color temperature by white detection and anobject color temperature by skin detection.

The second embodiment will be explained with reference to FIG. 7 showingthe white balance process of the image pickup device in this secondembodiment.

Color pixel output values Rw, Gw, and Bw of an image sensing element arecalculated backward by solving simultaneous equations (1) from SumCxWand SumCyW corresponding to color temperatures by white detection.

White balance coefficients WB_Rw, WB_Gw, and WB_Bw from white arecalculated from the values Rw, Gw, and Bw (Step S21):WB _(—) Rw=1.0/RwWB _(—) Gw=1.0/GwWB _(—) Bw=1.0/Bw  (12)

CxFromSkin and CyFromSkin along the white detection axis are calculatedfrom a color temperature CTempFromSkin by skin detection. Values Rs, Gs,and Bs are calculated from CxFromSkin and CyFromSkin by similarlysolving simultaneous equations. White balance coefficients WB_Rs, WB_Gs,and WB_Bs from the skin are calculated from the values Rs, Gs, and Bs(Step S22):WB _(—) Rs=1.0/RsWB _(—) Gs=1.0/GsWB _(—) Bs=1.0/Bs  (13)

White balance correction is performed on the basis of the two WBcoefficients for a color signal obtained within a block (center of aframe as shown in FIG. 4) designated in advance in the frame. Colordifference signals are generated from the corrected signals, and theaverages of the color difference signals are calculated (Step S23).Color difference signals are calculated from signals corrected based onthe white balance coefficients from white. The sums of the absolutevalues of the color different signals are averaged intoAveCrw, AveCbw  (14)Color difference signals are calculated from signals corrected based onthe white balance coefficients from the skin. The sums of the absolutevalues of the color different signals are averaged intoAveCrs, AveCbs  (15)

From these values, chromas are calculated (Step S25):ChromaW=sqrt(AveCrw1²+AveCbw1²)ChromaS=sqrt(AveCrs1²+AveCbs1²)  (16)

If the WB coefficients by white detection are correct (not deviate tothe skin),ChromaW=ChromaS  (17)If white detection deviates to the skin, the WB coefficients so act asto adjust the skin color to an achromatic color. When the human skinexists at the center of the frame,ChromaW<ChromaS  (18)

When equation (17) is established, the color temperature from whitesearch is output (Step S27). When inequality (18) is established, thefinal object color temperature is predicted using a weighted average,similar to the first embodiment (Step S26):CTempResult=k×CTempFromSkin+(1−k)×CTempFromWhite  (19)In equation (19), k, CTempResult, CTempFromSkin, and CTempFromWhite havethe same meanings as those in the first embodiment.

(19) means the greater deal of skin signals is detected, the muchimportance is CtempFromSkin regarded as. For example, If all signals inan picked up image are skin signals, CtempResult is adopted onlyCtempFromSkin obtained from the skin detection area. Therefore, thepresent embodiment can properly perform to adjust white balance of apicked up image even if white signals isn't detected in the picked upimage.

As described above, coefficients to adjust white balance are determined(Step S28).

In addition, weighted average between CtempFromWhite and CtempFromSkinmay be obtained not only in case of CtempFromWhite<CtemFromSkin, butalso in case of CtempFromWhite≧CtempFromSkin. This process is simplerthan the process as described above.

Furthermore, there is a possibility that the reliability of CtempResultis low because the detected skin signals will be a few in Step S25. Inthis case, the reliability of CtempResult may be higher by pre-processof Step S25 as described below. In the pre-process of Step S25, if thenumber of skin signals detected from the skin detecting area is smallerthan a predetermined number (for example, SkinSamplePercent=1%.), theprocess in Step S27 will be performed. Otherwise, the process in StepS25 will be performed.

As described above, the present embodiment can properly perform toadjust white balance of a picked up image.

(Third Embodiment)

The third embodiment is different from the first embodiment in themethod (Step S5 in FIG. 5) of mixing an object color temperature bywhite detection and an object color temperature by skin detection.

The total number of blocks of an image sensing element subjected to skindetection is represented byAllBlockNum  (20)

A ratio WBlockPercent of blocks determined to be white is calculatedusing AllBlockNum and the number SampleWNum of blocks falling within thewhite detection range:WBlockPercent=SampleWNum/AllBlockNum×100  (21)

The final object color temperature (CTempResult) is calculated by thefollowing weighted addition using the above ratio:

EXAMPLE

if (WBlockPercent>10%)CTempResult=CTempFromWhite  (22)elseCTempResult=WhiteRatio×CTempWhite+(1−WhiteRatio)×CTempFromSkinTo attain WhiteRatio=1.0 for WBlockPercent=10% and WhiteRatio=0.0 forWBlockPercent=0%, WhiteRatio is calculated by a linear function:WhiteRatio=a×WBlockPercent+b  (23)

The third embodiment adopts the skin color for white detection andchromatic color detection, but the same effects can also be obtained inthe use of the green of a leaf or the like or the blue of a blue sky orthe like, in addition to the skin color.

(Fourth Embodiment)

The fourth embodiment is different from the first embodiment in themethod (Step S5 in FIG. 5) of mixing an object color temperature bywhite detection and an object color temperature by skin detection.

In the fourth embodiment, when the photographing mode of a camera isdesignated to the portrait mode (person photographing mode), the whitebalance is adjusted using object color temperature information obtainedby skin detection.

Alternatively, when the photographing mode of the camera is the portraitmode, weighing of increasing the ratio of the coefficient k in themixing equation is executed.

As described above, according to the first to fourth embodiments, thefinal object color temperature is specified in consideration of colortemperature information from a skin color detection means in addition tocolor temperature information from a white detection means used in aconventional white balance device. Even when the white area is small ina close-up shot of a human face or the like, the color temperature canbe accurately determined.

A deviation to the skin color can be prevented for arelatively-low-illuminance object whose skin color has conventionallybeen misjudged as white and erroneously corrected to white.

For a bright object, the white detection range need not be narrowed,unlike the conventional white balance device. The white balance oftungsten light with a very high illuminance in a studio or the like canbe appropriately corrected.

[Other Embodiment]

The object of each embodiment is also achieved when a storage medium (orrecording medium) which stores software program codes for realizing thefunctions of the embodiment is supplied to a system or apparatus, andthe computer (or the CPU or MPU) of the system or apparatus reads outand executes the program codes stored in the storage medium. In thiscase, the program codes read out from the storage medium realize thefunctions of the above-described embodiments, and the storage mediumwhich stores the program codes constitutes the present invention. Thefunctions of the above-described embodiments are realized when thecomputer executes the readout program codes. Also, the functions of theabove-described embodiments are realized when an OS (Operating System)running on the computer performs part or all of actual processing on thebasis of the instructions of the program codes.

The functions of the above-described embodiments are also realized whenthe program codes read out from the storage medium are written in thememory of a function expansion card inserted into the computer or thememory of a function expansion unit connected to the computer, and theCPU of the function expansion card or function expansion unit performspart or all of actual processing on the basis of the instructions of theprogram codes.

When the present invention is applied to the storage medium, the storagemedium stores program codes corresponding to the above-described flowchart.

As has been described above, the above-described embodiments can alwaysprovide accurate white balance regardless of image sensing conditions.

The present invention is not limited to the above embodiments andvarious changes and modifications can be made within the spirit andscope of the present invention. Therefore, to apprise the public of thescope of the present invention the following claims are mode.

1. A white balance adjustment method comprising: a first colortemperature calculation step of calculating a first color temperaturefrom an image signal within a white detection range out of image signalsfrom an image sensing element; a second color temperature calculationstep of calculating a second color temperature from an image signalwithin a chromatic color detection range out of image signals from theimage sensing element; and a white balance adjustment step of adjustingwhite balance on the basis of the first and second color temperatures,wherein the first and second color temperatures are compared; when thefirst color temperature is substantially equal to the second colortemperature or the first color temperature is higher than the secondcolor temperature, the first color temperature is determined as a colortemperature of a light source; and when the second color temperature ishigher than the first color temperature, the second color temperature isdetermined as the color temperature of the light source.
 2. A whitebalance adjustment method comprising: a first color temperaturecalculation step of calculating a first color temperature from an imagesignal within a white detection range out of image signals from an imagesensing element; a second color temperature calculation step ofcalculating a second color temperature from an image signal within achromatic color detection range out of image signals from the imagesensing element; and a white balance adjustment step of adjusting whitebalance on the basis of the first and second color temperatures,wherein, the first and second color temperatures are compared; when thefirst color temperature is substantially equal to the second colortemperature or the first color temperature is higher than the secondcolor temperature, the first color temperature is determined as a colortemperature of a light source; and when the second color temperature ishigher than the first color temperature, weighted averages of the firstand second color temperatures are calculated on the basis of a ratio ofa white color range which occupies the image signal and a ratio of achromatic color, thereby determining the color temperature of the lightsource.
 3. A white balance adjustment method comprising: a first colortemperature calculation step of calculating a first color temperaturefrom an image signal within a white detection range out of image signalsfrom an image sensing element; a second color temperature calculationstep of calculating a second color temperature from an image signalwithin a chromatic color detection range out of image signals from theimage sensing element; and a white balance adjustment step of adjustingwhite balance on the basis of the first and second color temperatures,wherein a first white balance coefficient is calculated from the firstcolor temperature, the image signal being corrected by the first whitebalance coefficient, and a first chroma value is calculated from thecorrected image signal; a second white balance coefficient is calculatedfrom the second color temperature, the image signal being corrected bythe second white balance coefficient, and a second chroma value iscalculated from the corrected image signal; and the white balance isadjusted by a white balance coefficient corresponding to a larger one ofthe first and second chroma values.
 4. A white balance adjustment methodcomprising: a first color temperature calculation step of calculating afirst color temperature from an image signal within a white detectionrange out of image signals from an image sensing element; a second colortemperature calculation step of calculating a second color temperaturefrom an image signal within a chromatic color detection range out ofimage signals from the image sensing element; and a white balanceadjustment step of adjusting white balance on the basis of the first andsecond color temperatures, wherein a first white balance coefficient iscalculated from the first color temperature, the image signal beingcorrected by the first white balance coefficient, and a first chromavalue is calculated from the corrected image signals; a second whitebalance coefficient is calculated from the second color temperature, theimage signal being corrected by the second white balance coefficient,and a second chroma value is calculated from the corrected image signal;and weighted averages of the first and second chroma values arecalculated to determine a white balance coefficient.
 5. A white balanceadjustment method comprising: a first color temperature calculation stepof calculating a first color temperature from an image signal within awhite detection range out of image signals from an image sensingelement; a second color temperature calculation step of calculating asecond color temperature from an image signal within a chromatic colordetection range out of image signals from the image sensing element; anda white balance adjustment step of adjusting white balance on the basisof the first and second color temperatures, wherein a ratio of a whitecolor range which occupies the image signal is calculated; when theratio of the white color range is higher than a predetermined value, thefirst color temperature is determined as a color temperature of a lightsource; and when the ratio of the white color range is lower than thepredetermined value, weighted averages of the first and second colortemperatures are calculated to determine the color temperature of thelight source.
 6. A white balance adjustment method comprising: a firstcolor temperature calculation step of calculating a first colortemperature from an image signal within a white detection range out ofimage signals from an image sensing element; a second color temperaturecalculation step of calculating a second color temperature from an imagesignal within a chromatic color detection range out of image signalsfrom the image sensing element, wherein the chromatic color includes askin color; and a white balance adjustment step of adjusting whitebalance on the basis of the first and second color temperatures, whereinwhen a photographing mode of an image sensing apparatus is set to aperson photographing mode, a weight of the second color temperature isincreased; and a weighted average of the resultant second colortemperature and the first color temperature is calculated to determine acolor temperature of a light source.
 7. A white balance adjustmentapparatus comprising: a first color temperature calculation unit forcalculating a first color temperature from an image signal within awhite detection range out of image signals from an image sensingelement; a second color temperature calculation unit for calculating asecond color temperature from an image signal within a chromatic colordetection range out of image signals from the image sensing element; anda white balance adjustment unit for adjusting white balance on the basisof the first and second color temperatures, wherein the first and secondcolor temperatures are compared; when the first color temperature issubstantially equal to the second color temperature or the first colortemperature is higher than the second color temperature, the first colortemperature is determined as a color temperature of a light source; andwhen the second color temperature is higher than the first colortemperature, the second color temperature is determined as the colortemperature of the light source.
 8. A white balance adjustment apparatuscomprising: a first color temperature calculation unit for calculating afirst color temperature from an image signal within a white detectionrange out of image signals from an image sensing element; a second colortemperature calculation unit for calculating a second color temperaturefrom an image signal within a chromatic color detection range out ofimage signals from the image sensing element; and a white balanceadjustment unit for adjusting white balance on the basis of the firstand second color temperatures, wherein the first and second colortemperatures are compared; when the first color temperature issubstantially equal to the second color temperature or the first colortemperature is higher than the second color temperature, the first colortemperature is determined as a color temperature of a light source; andwhen the second color temperature is higher than the first colortemperature, weighted averages of the first and second colortemperatures are calculated on the basis of a ratio of a white colorrange which occupies the image signal and a ratio of a chromatic color,thereby determining the color temperature of the light source.
 9. Awhite balance adjustment apparatus comprising: a first color temperaturecalculation unit for calculating a first color temperature from an imagesignal within a white detection range out of image signals from an imagesensing element; a second color temperature calculation unit forcalculating a second color temperature from an image signal within achromatic color detection range out of image signals from the imagesensing element; and a white balance adjustment unit for adjusting whitebalance on the basis of the first and second color temperatures, whereina first white balance coefficient is calculated from the first colortemperature, the image signal being corrected by the first white balancecoefficient, and a first chroma value is calculated from the correctedimage signal; a second white balance coefficient is calculated from thesecond color temperature, the image signal being corrected by the secondwhite balance coefficient, and a second chroma value is calculated fromthe corrected image signal; and the white balance is adjusted by a whitebalance coefficient corresponding to a larger one of the first andsecond chroma values.
 10. A white balance adjustment apparatuscomprising: a first color temperature calculation unit for calculating afirst color temperature from an image signal within a white detectionrange out of image signals from an image sensing element; a second colortemperature calculation unit for calculating a second color temperaturefrom an image signal within a chromatic color detection range out ofimage signals from the image sensing element; and a white balanceadjustment unit for adjusting white balance on the basis of the firstand second color temperatures, wherein a first white balance coefficientis calculated from the first color temperature, the image signal beingcorrected by the first white balance coefficient, and a first chromavalue is calculated from the corrected image signal; a second whitebalance coefficient is calculated from the second color temperature, theimage signal being corrected by the second white balance coefficient,and a second chroma value is calculated from the corrected image signal;and weighted averages of the first and second chroma values arecalculated to determine a white balance coefficient.
 11. A white balanceadjustment apparatus comprising: a first color temperature calculationunit for calculating a first color temperature from an image signalwithin a white detection range out of image signals from an imagesensing element; a second color temperature calculation unit forcalculating a second color temperature from an image signal within achromatic color detection range out of image signals from the imagesensing element; and a white balance adjustment unit for adjusting whitebalance on the basis of the first and second color temperatures, whereina ratio of a white color range which occupies the image signal iscalculated; when the ratio of the white color range is higher than apredetermined value, the first color temperature is determined as acolor temperature of a light source; and when the ratio of the whitecolor range is lower than the predetermined value, weighted averages ofthe first and second color temperatures are calculated to determine thecolor temperature of the light source.
 12. A white balance adjustmentapparatus comprising: a first color temperature calculation unit forcalculating a first color temperature from an image signal within awhite detection range out of image signals from an image sensingelement; a second color temperature calculation unit for calculating asecond color temperature from an image signal within a chromatic colordetection range out of image signals from the image sensing element,wherein the chromatic color includes a skin color; and a white balanceadjustment unit for adjusting white balance on the basis of the firstand second color temperatures, wherein when a photographing mode of animage sensing apparatus is set to a person photographing mode, a weightof the second color temperature is increased; and a weighted average ofthe resultant second color temperature and the first color temperatureis calculated to determine a color temperature of a light source.